Furuno GP-7000F - Manual (Page 113)

10. VIDEO SOUNDER OPERATION
10-27
Fish school density
If two schools appear with the same color at different depth, the one in deeper
water is denser because the ultrasonic wave attenuates as it propagates and the
fish school in deep water tends to be displayed in a weaker color.
Fish echo
Less Reddish
(Sparse echo)
Reddish
(Dense echo)
Difference in
signal strength
Weak Echo
Strong
Echo
Fish school density
Plankton
A plankton layer, a likely place to find fish, is displayed in green or blue dots. It
usually descends in the day and rises at night.
Fish
School
Plankton
Plankton
Current rip
When two ocean currents meet with different speeds, directions and water
temperatures, a current rip develops. A current rip’s on-screen appearance is as
shown below.
Current
rip
Current rip